The removal of carbon dioxide from various gases is important in many areas. For example, many hydrocarbon process streams contain carbon dioxide impurities which can contaminate downstream processes such as propylene polymerization. Other areas of interest involve closed ecological systems such as submarines, diving apparati and the like where it is imperative that the carbon dioxide exhaled by the occupants be removed from the remaining air.
One method that has been used to remove carbon dioxide from gaseous streams involves the use of liquids, such as solutions containing ethanolamine, ammonia, soda, carbonates and lyes. However, such systems are expensive and are not simple to regenerate. These systems are also subject to physical loss by carryover and entrainment in the gaseous phase. The solutions tend to be corrosive to conventional processing equipment and carryover only exacerbates this problem.
Another approach to the problem has been to use solid absorbent materials such as so-called molecular sieves, calcium oxide, finely divided micro-porous silver oxide dispersed and in admixture with aluminum oxide, and supported cogels of divalent and trivalent metals such as that disclosed in U.S. Pat. No. 3,141,729, issued July 21, 1964. However, these special substances are ordinarily quite expensive. In addition, the molecular sieves, for example, have low capacity for carbon dioxide and also co-absorb other gases which either contaminate the carbon dioxide upon its removal or require pre-processing of the gas stream passing through the adsorbent.
Another approach has been to use alkali metal carbonates coated on carriers or admixed with alumina to absorb carbon dioxide. U.S. Pat. No. 3,865,924 issued Feb. 11, 1975, disclosed the use of a synergistic mixture of carbonate and alumina. Since the sorption reaction is as follows: EQU K.sub.2 CO.sub.3 +CO.sub.2 +H.sub.2 O.fwdarw.2KHCO.sub.3
it can be seen that water must be supplied before the process is effective. This addition of water is detrimental to many process streams.